Several therapeutic and diagnostic applications use ultrasound energy. For example, ultrasound energy can be used to enhance the delivery and therapeutic effect of various therapeutic compounds. See e.g., U.S. Pat. Nos. 4,821,740, 4,953,565 and 5,007,438, the entire disclosure of which is hereby incorporated by reference herein. In some applications, it is desirable to use an ultrasound catheter to deliver the ultrasound energy and/or therapeutic compound to a specific treatment site in the body. Such an ultrasound catheter typically comprises an elongate member configured for advancement through a patient's vasculature. An ultrasound assembly is mounted along the distal end portion of the elongate member and is adapted for emitting ultrasound energy. The ultrasound catheter may include a delivery lumen for delivering the therapeutic compound to the treatment site. In this manner, the ultrasound energy can be emitted at the treatment site to enhance the desired therapeutic effects and/or delivery of the therapeutic compound.
In one particular application, ultrasound catheters have been successfully used to treat human blood vessels that have become occluded by plaque, thrombi, emboli or other substances that reduce the blood carrying capacity of the vessel. See e.g., U.S. Pat. No. 6,001,069, the entire disclosure of which is hereby incorporated by reference herein. To remove the blockage, the ultrasound catheter is advanced through the patient's vasculature to deliver solutions containing dissolution compounds directly to the blockage site. To enhance the therapeutic effects of the dissolution compound, ultrasound energy is emitted into the compound and/or the surrounding tissue.
In another application, ultrasound catheters may be used to perform gene therapy on an isolated region of a blood vessel or other body lumen. For example, as disclosed in U.S. Pat. No. 6,135,976, the entire disclosure of which is hereby incorporated by reference herein, an ultrasound catheter can be provided with one or more expandable members for occluding a section of the body lumen at a treatment site. A gene therapy composition is delivered to the treatment site through the delivery lumen of the catheter. The ultrasound assembly is used to emit ultrasound energy at the treatment site to enhance the entry of the gene composition into the cells in the body lumen.
In addition to the applications discussed above, ultrasound catheters may be used for a wide variety of other purposes, such as, for example, delivering and activating light activated drugs with ultrasound energy (see e.g., U.S. Pat. No. 6,176,842, the entire disclosure of which is hereby incorporated by reference herein).
Over the years, numerous types of ultrasound catheters have been proposed for various therapeutic purposes. However, none of the existing ultrasound catheters is well adapted for effective use within small blood vessels in the distal anatomy. For example, in one primary shortcoming, the region of the catheter on which the ultrasound assembly is located (typically along the distal end portion) is relatively rigid and therefore lacks the flexibility necessary for navigation through difficult regions of the distal anatomy. Furthermore, it has been found that it is very difficult to manufacture an ultrasound catheter having a sufficiently small diameter for use in small vessels while providing adequate pushability and torqueability. Still further, it has been found that the distal tip of an ultrasound catheter can easily damage the fragile vessels of the distal anatomy during advancement through the patient's vasculature.
Accordingly, an urgent need exists for an improved ultrasound catheter that is capable of safely and effectively navigating small blood vessels. It is also desirable that such a device be capable of delivering adequate ultrasound energy to achieve the desired therapeutic purpose. It is also desirable that such a device be capable of accessing a treatment site in fragile distal vessels in a manner that is safe for the patient and that is not unduly cumbersome. The present invention addresses these needs.